Apparatus and methods for wake-limiting with an inter-device communication link

ABSTRACT

Methods and apparatus for limiting wake requests from one device to one or more other devices. In one embodiment, the requests are from a peripheral processor to a host processor within an electronic device such as a mobile smartphone or tablet which has power consumption requirements or considerations associated therewith. In one implementation, the peripheral processor includes a wake-limiting procedure encoded in e.g., its software or firmware, the procedure mitigating or preventing continuous and/or overly repetitive “wake” requests from the peripheral processor.

RELATED APPLICATIONS

This application is related to commonly owned and co-pending U.S. patentapplication Ser. No. 14/879,027 entitled “METHODS AND APPARATUS FORMANAGING POWER WITH AN INTER-PROCESSOR COMMUNICATION LINK BETWEENINDEPENDENTLY OPERABLE PROCESSORS”, filed Oct. 8, 2015, Ser. No.14/879,024 entitled “METHODS AND APPARATUS FOR RUNNING AND BOOTING ANINTER-PROCESSOR COMMUNICATION LINK BETWEEN INDEPENDENTLY OPERABLEPROCESSORS”, filed Oct. 8, 2015, Ser. No. 14/879,030 entitled “METHODSAND APPARATUS FOR RECOVERING ERRORS WITH AN INTER-PROCESSORCOMMUNICATION LINK BETWEEN INDEPENDENTLY OPERABLE PROCESSORS”, filedOct. 8, 2015, Ser. No. 14/856,283 entitled “METHODS AND APPARATUS FORAGGREGATING PACKET TRANSFER OVER A VIRTUAL BUS INTERFACE”, filed Sep.16, 2015, and Ser. No. 14/870,923 entitled “METHODS AND APPARATUS FORCONTROLLED RECOVERY OF ERROR INFORMATION BETWEEN INDEPENDENTLY OPERABLEPROCESSORS” filed Sep. 30, 2015, and commonly owned and co-pending U.S.Provisional Patent Application Ser. No. 62/175,174 entitled “METHODS ANDAPPARATUS FOR SYNCHRONIZING UPLINK AND DOWNLINK TRANSACTIONS ON ANINTER-PROCESSOR COMMUNICATION LINK” filed Jun. 12, 2015, each of theforegoing incorporated herein by reference in its entirety.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND

1. Technical Field

The disclosure relates generally to the field of electronics devices, aswell as networks thereof. More particularly, in one exemplary aspect,the disclosure is directed to methods and apparatus for implementing aninter-device (e.g., processor communication or IPC link between two (ormore) independently operable devices. Various aspects of the presentdisclosure are directed to, inter alia, power management.

2. Description of Related Technology

Many electronic devices, such as e.g., mobile devices and portablecomputing devices, include integrated circuits such as e.g., anApplication Processor (AP) system on a chip (SoC), which is a mainprocessor chip designed to support one or more applications running inthe operating environment of the electronic device (e.g., hostprocessor). The AP is in data communication with other peripheralchipsets (e.g., processors) of the device, such as e.g., cellular and/orWi-Fi chipsets via a memory-mapped interconnect and/or bus.

Various bus architectures and techniques have evolved over time whichenable handling of increasingly faster data rates and provide higherlevels of data throughput for the AP and/or peripheral processors. Onesuch example is Peripheral Component Interconnect Express (PCIe); seee.g., PCI Express Base Specification Revision 3.1 dated Oct. 8, 2014.PCIe is a high-speed serial computer expansion bus standard designed toreplace older PCI and similar bus standards. In terms of architecture,PCIe is based on point-to-point connectivity with separate serial linksconnecting each endpoint peripheral component (e.g., graphics card,memory, Wi-Fi, cellular, etc.) to the root complex or host processor(including the AP).

Communication between the AP and the peripheral chipsets via PCIe hasmany desirable attributes in terms of, inter alia, performance andflexibility. However, PCIe (as well as some other existing“computer-centric” bus technologies) suffer certain disabilities,especially from the standpoint of portable consumer electronic deviceimplementations. Specifically, as noted above, extant PCIe technologieswere developed for use within desktop, server, and laptop computers,which are to varying degrees agnostic to many electrical powerconsiderations affecting smaller portable devices. Desktops and servers(and to a lesser degree laptops) are less concerned with electricalpower consumption/conservation, and more concerned with bus performance,ability to “hot plug”, and the like. Accordingly, implementing atechnology such as PCIe which, in its current incarnation, both (i)consumes significant electrical power during operation, and (ii) haslimited power management infrastructure (e.g., application or hostprocessor and chipset “sleep” states, and management of data andtransactions during such sleep states), is generally unsuitable forportable consumer electronics applications where power consumption andbattery conservation are critical (such as e.g., cellular- andWi-Fi-enabled smartphones, tablets, “phablets”, portable media players,etc.). Further, other device components, such as the AP and theperipheral chipsets each consume additional electrical power duringoperation.

In order to limit power consumption within the electronic device, bothof the AP and the peripheral chipsets may be automatically andindependently switched between one or more lower power states (e.g., anawake-low power state, a sleep-low power state, etc.) during periods ofnon-use and a higher power state (e.g., an awake-high power state)during periods of use. There is generally a power consumption versuslatency trade-off, where the lowest power state (e.g., sleep-low power)consumes the least amount of power but requires a longer duration oftime to return to the fully awake state. Further, the energy costassociated with switching from the sleep-low power state to the fullyawake state is potentially greater than that associated with switchingfrom the awake-low power state to the fully awake state. Therefore it istypically desirable that the AP and/or the peripheral chipsets entertheir lowest power states only during longer periods of non-use.

In some instances, user inactivity can initiate switching from a fullyawake state to a lower power state. For example, after a shorter periodof user inactivity, the AP may be switched to the awake-low power state,while after a longer period of user inactivity, the AP may be switchedto the sleep-low power state. In other instances, activity orcommunication from the AP and the peripheral chipsets can initiateswitching from a lower power state to a fully awake state (e.g., anawake-high power state) if the other chip is in a lower power state. Forexample, activity or communication from the AP, such as e.g., an uplinkrequest, can initiate switching of the peripheral chipset in a lowerpower state to a fully awake state and/or activity or communication fromthe peripheral chipset, such as e.g., a downlink request, can initiateswitching of the AP in a lower power state to a fully awake state. Inthe foregoing examples, mechanisms for causing switching and transitionto a fully awake state may include built-in mechanisms from theinterconnect (e.g., PCIe), such as e.g., PCIe WAKE# general purposeinput/output (GPIO), or out-of-band mechanisms independent of theinterconnect, such as e.g., a proprietary GPIO.

The interconnect (e.g., PCIe) between the AP and the peripheral chipsets may be controlled by a software layer, referred to as aninter-processor communication (IPC) layer. The IPC layer may definevarious power states to achieve different power versus latencytradeoffs. In some examples, the IPC layer may allow the AP to enter thelowest power state (e.g., sleep-low power), while in other examples theIPC layer may prevent the AP from entering the lowest power state. Theperipheral chipset may signal the IPC layer to switch from a lower powerstate to a higher power state. Thus, signaling from the peripheral tothe IPC layer may subsequently signal the AP to switch from a lowerpower state to a higher power state.

The AP may be responsible for initiating all uplink and downlinktransactions. Thus, peripheral chipsets are only able to send a downlinkdata packet when the AP is in the awake-high power state and enables oropens the corresponding interconnect pathway (e.g., a “unidirectionalpipe”). In a related aspect, the peripheral chipsets may signal to theAP to open an interconnect pathway, thereby requesting “wake up” (i.e.,switching from a lower power state to a higher power state) of the AP ifthe AP is in a lower power state. In some cases, the peripheral chipsetmay continuously or repeatedly request “wake up” of the AP if there isno response from the AP and/or if there is an error in transfer of thedata packet, thereby causing unnecessary power consumption by theperipheral chipset, the interconnect, and/or the AP. Such operationalscenarios and requirements are quite common with the aforementionedcellular devices, media players, and similar devices.

Hence, there is a need for improved apparatus and associated methodswhich can leverage the high data throughput and other desirableattributes of bus technologies such as PCIe (and other “memory mapped”technologies), yet support the requirements of rigorous power managementand conservation, as well as the ability to support various combinationsof operational sleep states or other reduced-power modes by variouschips or chipsets within the device.

SUMMARY

The present disclosure satisfies the foregoing needs by providing, interalia, methods and apparatus for implementing an inter-device (e.g.,inter-processor communication (IPC)) link between two (or more) devices,such as two or more independently operable processors. (e.g., a hostprocessor and a peripheral processor), and limiting “wake” of a firstdevice by a second device when the first device is in a lower powerstate than the second device.

In one aspect, a method performed by a first device to limit wakerequests to a second device is disclosed. In one embodiment, the methodincludes: detecting a condition for determining whether to send a wakerequest to the second device; determining that one or more data unitsare to be transferred from the first device to the second device overone or more data lines; for each data line of the one or more datalines, determining whether a number of previous wake requests associatedwith the data line is less than a wake limit threshold; and in responseto determining that at least one of the data lines is associated with anumber of previous wake requests that is less than the wake limitthreshold, sending a wake request to the second device.

In one variant, the first and second devices include digital processors,and the detecting the condition for determining whether to send the wakerequest to the second device comprises detecting that the second devicehas switched from a first power state to a second, lower power state.

In another variant, detecting the condition for determining whether tosend the wake request to the second device comprises determining that anew data unit is to be transferred from the first device to the seconddevice over a first data line of the one or more data lines. In oneimplementation of this variant, the method further includes, in responseto determining that the new data unit is to be transferred from thefirst device to the second device over the first data line, setting anumber of previous wake requests associated with the first data line tozero.

In yet a further variant, the method includes, for each data line of theone or more data lines, detecting that the data line is enabled, andsetting a number of previous wake requests associated with the data lineto zero.

In another variant, the method further includes setting a number ofprevious wake requests associated with the first data line to zero inresponse to determining that a first data unit of the one or more dataunits is transferred from the first device to the second device over afirst data line of the one or more data lines.

In another aspect of the disclosure, processor apparatus adapted for usein a portable device is disclosed. In one embodiment, the processorapparatus includes: a first digital processor; and storage apparatus indata communication with the first digital processor. In one variant, thestorage apparatus includes a plurality of computer readable instructionsconfigured to, when executed by the first digital processor, cause thefirst digital processor to: determine that one or more data units are tobe transferred from the first processor to the second processor over oneor more data lines; for each data line of the one or more data lines,determine whether one or more previous wake requests associated with thedata line meets a prescribed criterion (e.g., is less than a wake limitthreshold); and in response to determining that at least one of the datalines is associated with a number of previous wake requests that meetsthe criterion (e.g., is less than the wake limit threshold), send a wakerequest to the second processor.

In one variant, the plurality of computer readable instructions arefurther configured to, when executed by the first digital processor,cause the first digital processor to detect a condition fordetermination whether to send the wake request to the second processor,the detection comprising detection that the second processor hasswitched from a first power state to a second, lower power state.

In another variant, the plurality of computer readable instructions arefurther configured to, when executed by the first digital processor,cause the first digital processor to, in response to a determinationthat one or more new data units is to be transferred from the firstprocessor to the second processor over the first data line, set a numberof previous wake requests associated with the first data line to zero.

In yet another variant, the plurality of computer readable instructionsare further configured to, when executed by the first digital processor,cause the first digital processor to, for each data line of the one ormore data lines, detect that the data line is enabled, and set a numberof previous wake requests associated with the data line to zero.

In another aspect of the disclosure, a portable electronic deviceconfigured for power management is disclosed. In one embodiment, theportable electronic device is a wireless-enabled mobile smartphone, andincludes: a first processor; a second processor in data communicationwith the first processor via one or more data lines; and storageapparatus in data communication with at least the first digitalprocessor, the storage apparatus comprising a plurality of computerreadable instructions. In configured to, when executed by the firstdigital processor, cause the first digital processor to: upon receipt ofdata indicating a state change, determine that one or more data unitsare to be transferred from the first processor to the second processorover the one or more data lines; for each data line of the one or moredata lines, determine that a number of previous wake requests associatedwith the data line is less than a wake limit threshold; and based atleast on the determination that at least one of the data lines isassociated with a number of previous wake requests less than the wakelimit threshold, send a wake request to the second processor.

In a further aspect of the disclosure, a method of operating awireless-enabled portable device is disclosed. In one embodiment, themethod includes avoiding unnecessary “wake ups” of one or moreintegrated circuit devices of the portable device (e.g., an applicationprocessor) by other peripheral integrated circuits, such as the baseband(wireless) chip set.

In another aspect, processing logic which can leverage the high datathroughput and other desirable attributes of bus technologies such asPCIe (and other “memory mapped” technologies) is disclosed. In oneembodiment, the logic comprises software and/or firmware operative to beexecuted by integrated circuit digital processors of a portable device.Such logic also in one implementation supports the requirements ofrigorous power management and conservation, as well as the ability tosupport various combinations of operational sleep states or otherreduced-power modes by various chips or chipsets within the portabledevice.

In a further aspect of the disclosure, integrated circuity configured toimplement “intelligent” power and state management is disclosed. In oneembodiment, the integrated circuitry includes one or more semiconductivedie with digital processor apparatus disposed thereon and configured tocommunicate with one or more other integrated circuit devices within acommon platform (e.g., mobile wireless device).

In yet another aspect, a computer-readable apparatus is disclosed. Inone embodiment, the apparatus includes a storage medium configured toretain one or more computer programs in a non-transitory fashion, andwhich is accessible by a digital processing apparatus.

Other features and advantages of the present disclosure will immediatelybe recognized by persons of ordinary skill in the art with reference tothe attached drawings and detailed description of exemplary embodimentsas given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a logical block diagram of one exemplary apparatus useful forillustrating various principles described herein.

FIG. 2 is a logical block diagram of one exemplary physical businterface useful in conjunction with the various principles describedherein.

FIG. 3 is a logical block diagram of an exemplary run time operationstate machine useful in conjunction with the various describedembodiments.

FIG. 4 is a logical flow diagram illustrating an exemplary embodiment ofa power management process for independently operable processors, inaccordance with the present disclosure.

FIG. 5 is a logical flow diagram illustrating an exemplary embodiment ofa power management process for independently operable processors in acondition where the host processor switches to a lower power state, inaccordance with the present disclosure.

FIG. 6 is a logical flow diagram illustrating an exemplary embodiment ofa power management process for independently operable processors in acondition where the host processor is in a lower power state, inaccordance with the present disclosure.

FIG. 7 is a logical flow diagram illustrating an exemplary embodiment ofa power management process for a wake-limiting procedure, in accordancewith the present disclosure.

FIGS. 8A and 8B are data flow diagrams illustrating communicationsbetween a peripheral device and a host processor during a wake-limitingProcedure, in accordance with one implementation of the presentdisclosure.

All Figures © Copyright 2014-2016 Apple, Inc. All rights reserved.

DETAILED DESCRIPTION

Reference is now made to the drawings, wherein like numerals refer tolike parts throughout.

Detailed Description of Exemplary Embodiments

Exemplary embodiments of the present disclosure are now described indetail. While these embodiments are primarily discussed in the contextof an inter-processor communication (IPC) link (for example, of the typedescribed within commonly owned and co-pending U.S. patent applicationSer. No. 14/856,283 entitled “METHODS AND APPARATUS FOR AGGREGATINGPACKET TRANSFER OVER A VIRTUAL BUS INTERFACE”, filed Sep. 16, 2014,previously incorporated by reference in its entirety), it will berecognized by those of ordinary skill that the present disclosure is notso limited. In fact, the various aspects of the disclosure are useful inany device or network of devices that is configured to incorporate andcoordinate multiple independent devices (e.g. processing elements),including e.g., in an inter-platform fashion (e.g., across two or morediscrete host devices) as is disclosed herein.

Various embodiments described herein may be used in conjunction withpower management schemes such as those described within commonly ownedand co-pending U.S. patent application Ser. No. 14/879,024 entitled“METHODS AND APPARATUS FOR RUNNING AND BOOTING AN INTER-PROCESSORCOMMUNICATION LINK BETWEEN INDEPENDENTLY OPERABLE PROCESSORS”, filedOct. 8, 2015, previously incorporated by reference in its entirety.

Additionally, various embodiments described herein may also be used inconjunction with error recovery schemes, such as those described withincommonly owned and co-pending U.S. patent application Ser. No.14/879,030 entitled “METHODS AND APPARATUS FOR RECOVERING ERRORS WITH ANINTER-PROCESSOR COMMUNICATION LINK BETWEEN INDEPENDENTLY OPERABLEPROCESSORS”, filed Oct. 8, 2015, previously incorporated by reference inits entirety.

Further, while the following embodiments describe specificimplementations of e.g., dedicated address spaces, legacy supportcapabilities, and specific protocols, those of ordinary skill in therelated arts will readily appreciate that such descriptions are purelyillustrative.

Moreover, while exemplary implementations are described in the contextof the PCIe protocol, it will be appreciated that the various featuresand techniques described herein can be applied to and implemented usingother bus protocols, including especially those based on memory-mappedschemes.

Exemplary Inter-Processor Communications Link

As previously noted, bus techniques have evolved which are able tohandle faster data rates and provide higher levels of data throughput.One such example is Peripheral Component Interconnect Express (PCIe).PCIe has historically been used as a high-speed serial computerexpansion bus technology; PCIe is based on point-to-point connectivitywith separate serial links connecting each peripheral endpoint component(e.g., graphics card, memory, Wi-Fi, cellular, etc.) to the root complexor host processor (including and/or coupled to the application processor(AP)). However, existing PCIe technologies, as well as the variouschipsets within the device, consume significant power and therefore maybe unsuitable for many portable consumer electronics applications.

Within this context, exemplary methods and apparatus are now describedwhich support an inter-processor communication (IPC) link between two(or more) independently operable processors (e.g., the AP and peripheralchipsets). The following discussions will be described in reference to a“root complex” (RC) (or “host”) processor, and an “endpoint” (EP) (or“peripheral”) processor. For reasons which will become apparent below,it is appreciated that the designation as to host or peripheralprocessor is used to simplify and/or clarify the following explanations,and does not imply existing host or peripheral functionality, or thatsuch roles cannot be reversed.

In one aspect, the IPC protocol is based on a “shared” memory interfacefor run-time processing (i.e., the independently operable processorseach share, either virtually or physically, a common memory interface).In one such embodiment, the shared memory interface provides amulti-channel IPC path for high throughput transfers. In one exemplaryimplementation, the shared memory interface remains functional when anyone of the independently operable processors is active, even when one ormore of the remaining independently operable processors are asleep(i.e., in a low power state), powered down, powered off, etc.

In another aspect, the IPC link is configured to control, inter alia,sleep procedures or switching between lower power states to higher powerstates (as defined separately for the host and peripheral processors),and error handling.

As used herein, the term “logical” or “virtual” are interchangeably usedto refer to, without limitation, an abstraction (typically performed insoftware or machine logic) to represent physical mechanisms, attributesor functionalities as a data structure. For example, as used herein a“logical bus interface”, “virtual bus interface”, etc. refers generallyto an abstraction or representation of a bus interface as a series ofdata structures. In contrast, as used herein a “physical bus interface”refers to the physical mechanisms, attributes or functionalities of aphysically tangible bus interface.

As used herein, the term “in-band” refers without limitation to datatransactions which are transacted within a logical or physicalinterface, and which affect the mechanisms, attributes orfunctionalities of the logical or physical interface. In contrast, theterm “out-of-band” refers to data transactions which are not transactedwithin a logical or physical interface, and which affect the mechanisms,attributes or functionalities of the logical or physical interface.

FIG. 1 illustrates exemplary apparatus 100 (e.g., an electronic device)useful for illustrating various principles described herein. As shown,the apparatus 100 includes a first processor 102A and a second processor102B, and a physical bus interface 104 that is configured to implementan inter-processor communication (IPC) link between two (or more)independently operable processors.

In one implementation, the first processor 102A includes an applicationsprocessor (AP). As shown in FIG. 1, the first processor 102A is coupledto a Root Complex (RC) 106A which functions as the host of the IPC bus.

In one implementation, the second processor 102B includes a wirelessmodem (e.g., Wi-Fi or cellular peripheral processor). As used herein,the term “wireless” includes, without limitation, Long TermEvolution/Advanced (LTE and LTE-A) technology, devices implementingIEEE-Std. 802.11 (any variants thereof), PAN technology such as e.g.,Bluetooth or IEEE Std. 802.15.4, “ZigBee” or other simplified or “IoT(Internet of Things)” interfaces, near field communication/RFID, WiMAX(IEEE 802.16), WMANs, 3G cellular (e.g., WCDMA, 3GPP, 3GPP2, and GSM andimprovements thereon, and ISM band devices, as well as combinations ofthe foregoing (e.g., where NFC is used to enable rapid negotiationbetween devices to enable subsequent communications over a Bluetooth orWi-Fi Direct link).

In other embodiments, the second processor 102B may be e.g., a mediaprocessor, or other network processing element. As shown in FIG. 1, thesecond processor 102B is coupled to an endpoint (EP) 106B whichfunctions as the peripheral of the IPC bus.

As shown, both the first and the second processors (102A, 102B) are eachcoupled to a non-transitory computer readable medium (e.g., dynamicrandom access memory (DRAM)) (108A, 108B) and a memory management unit(MMU) (110A, 110B). The non-transitory computer readable medium isconfigured to store computer readable instructions (e.g., in the form ofone or more computer programs) for execution by their respectiveprocessors.

As shown in FIG. 2, the physical bus interface 104 is loosely based onthe Peripheral Component Interconnect Express (PCIe) standard (e.g., asis described in “PCI Express Base Specification Revision 3.0” publishedNov. 10, 2010, and “ECN L1 PM Substates with CLKREQ” approved Aug. 23,2012). Those of ordinary skill in the related arts, given the contentsof the present disclosure, will readily appreciate that other businterface standards may be substituted with equal success. Variousmodifications to the underlying physical bus interface 104 (andprotocols used therewith) to support IPC functionality is described ingreater detail hereinafter.

In the exemplary embodiment, the physical bus interface 104 is apoint-to-point communication channel between two IPC ports (the RC andEP) allowing both to send/receive access requests (configurationread/write, I/O read/write, memory read/write) and interrupts. At thephysical level, a link is composed of one or more lanes (one lane 200 isshown in FIG. 2), each lane having receive and transmit component(pcie_rx, pci_tx). Each lane is a full-duplex byte stream, transportingdata packets in eight-bit ‘byte’ formats, between the RC and EP of alink, in both directions simultaneously. The physical IPC link 104 cansupport multiple logical links (or virtual bus interfaces) representingmultiple ongoing data sessions.

In one such embodiment, each virtual bus interface further includes oneor more “sessions” which are a persistent and/or semi-persistent set ofdata transactions (e.g., datagrams) between two logical endpoints. Insome implementations, the session may include “stateful” transactions(i.e., the data transactions are based on a current state of thesession), and/or “stateless” transactions (i.e., the data transactionsare not based on a current state of the session).

Exemplary Run Time Processing

In one aspect, the aforementioned computer readable instructions, whenexecuted by at least one of the first or second processors (102A, 102B)are configured to transact data via a run-time processing protocol thatis based on a shared memory architecture. FIG. 3 illustrates oneexemplary embodiment of a run-time IPC state machine 300. In theexemplary embodiment, the first and second processor share a sharedmemory interface that includes a memory mapped input/output (MMIO)space.

The state machine comprises four (4) states in the illustratedembodiment; i.e., an UnInit state 302, an Init state 304, a Runningstate 306, and an Error state 308. In one exemplary variant, the four(4) states are controlled by two registers in the MMIO: IPC Status, andIPC Control. IPC Status is read-only for the host processor andread/write for the peripheral processor and reflects the peripheralprocessor's IPC state machine. IPC Control is write-only for the hostand read-only for the peripheral processor. IPC Control allows the hostprocessor to trigger IPC state machine transitions. Writing to IPCControl triggers an interrupt for the peripheral processor.

In the exemplary embodiment of FIG. 3, the run-time IPC state machinestarts in the UnInit state 302 (e.g., a default state from reset,power-down, power-off, etc.) When the host processor writes aninitialize command to the IPC Control register, the state machinechanges to the Init state 304. Responsively, the peripheral processorsets up and initializes its local data structures, and updates the IPCStatus register to signal that the Init state 304 has completed. In someembodiments, the peripheral processor may additionally notify the hostprocessor (e.g., with a message signaled interrupt (MSI) i.e., aPCIe-based mechanism that allows the peripheral processor to send aninterrupt to the host processor). Concurrently, the host processor caninitialize its own data structures; when the host processor receives thenotification, it checks the IPC Status register to detect the completedchange to Init state 304.

From the Init state 304, the host processor updates the shared memoryinterface (e.g., the MMIO register Context Information Address) andtriggers the transition to the Running State 306 by writing a runcommand to the IPC Control register. Responsively, the peripheralprocessor reads the Context Information and updates the IPC Statusregister to “Running”.

As described in greater detail hereinafter, in the Running state 306,data transfers can take place between the host and the peripheralprocessor; however, in the event of an error condition on either thehost or the peripheral processor, the IPC state machine transitions tothe Error State 308. The host informs the peripheral processor of anerror by writing an error flag to the IPC Control register. In contrast,the peripheral processor informs the host processor of an error(internal or host initiated), by updating the IPC Status register toError.

From the Error state 308, the peripheral processor clears its currentContext Information Address and terminates further host memory access.In some cases, the peripheral processor may store a mirror copy of a fewcritical peripheral processor registers; i.e. Execution Stage Mirror andIPC Status Mirror, in the host memory (in a location specified fordevice information). Once the peripheral processor has the deviceinformation address, it updates the mirror copy of these registers inhost memory each time the local register changes, followed by a MSI. TheIPC Status Mirror is updated by the peripheral processor as part of theRunning and Error States (306, 308).

Referring back to the Running state 306 of FIG. 3, in one exemplaryembodiment, data transfers are performed as a series of datatransactions over unidirectional “pipes”. A pair of pipes creates abi-directional interface. While the following discussion is providedwithin the context of a “full-duplex” scheme, those of ordinary skill inthe related arts will readily appreciate that the described protocolsmay be substituted with equal success with so-called “half duplex”schemes.

In one exemplary embodiment, a client service (e.g., control, data,trace, etc. associated with a data session) is associated with a singleinterface i.e., a pair of pipes. Each client service input/output (I/O)may be composed of multiple so-called “transfer descriptors” (TD). Forexample, a single TD may describe a physically contiguous memory buffer,accessible by the host/peripheral processor over the communication link.

Each pipe (i.e., data stream) is associated with one “transferdescriptor ring” (TDR). The TDR data structure resides in host processormemory and is accessible by the peripheral processor. Each TDR isdescribed by a head pointer and a tail pointer, and encompasses one ormore TD; each TD includes: an address of a buffer in host memory, a sizeof the buffer, a next count that indicates the number of TDs remainingin an I/O transfer, and a completion status. The head pointer points tothe next empty slot in the TDR, whereas the tail pointer points to theaddress of next TD which the peripheral will process. The head pointeris written by the host and read by the peripheral. The tail pointer isread by the host and written by the peripheral. All TDs and associateddata buffers between the tail pointer and the head pointer areassociated with the peripheral processor. When the head pointer is equalto the tail pointer, the TDR is empty.

The peripheral processor provides an array of so-called “doorbell”registers, and a so-called “head pointer doorbell array” (HPDA) which isfurther indexed by pipe number. The host processor notifies theperipheral processor of a new TD in a TDR by writing the head pointervalue in the doorbell register at a pipe number offset inside the HPDA.Similarly, the host provides a so-called “tail pointer array” (TPA) inhost memory that is indexed by pipe number, which is updated by theperipheral processors with tail pointer values to indicate completion ofa TD.

The TDR is valid while the pipe is open or enabled. Pipes can be openedor closed based on appropriate messaging. For example, in one suchimplementation, an Open Message provides the address of the TDR and itssize, whereas a Close Message completion may “reap” the TDR (e.g.,enabling the data to be overwritten or allocated to other purposes,etc.). When a pipe is not open, its corresponding values within the TPAand HPDA are not relevant (or otherwise disregarded).

In one aspect, the host processor controls the state of the pipe via amessaging data structure. In one exemplary embodiment, the messagingdata structure is queued according to a message ring (MR), whichoperates in a manner similar to the aforementioned TDR. Specifically,the MR is described by a message tail pointer (MTP), a message headpointer (MHP), and a message head pointer doorbell (MHPD). Wheninitializing the IPC state machine, the processor configures the MR, andsets the MR base address in the MTP, and update context informationwhich is configured to cause the peripheral processor to read the MRbase address in the MHPD and transition the Run Time IPC State Machineof FIG. 3 to the Running State 306. Thereafter, the host can transactmessages with the peripheral processor.

During run time operation, every time the host has a new message tosend, it checks whether there is space in the MR for a message request.If so, a new message entry is created at the MHP and the head pointervalue is updated. The new head pointer value is written to the MHPD.When the peripheral processor has consumed the message, it updates thestatus of the message and then updates the MTP. Additionally, theperipheral processor sends an MSI.

Various other modifications and/or permutations of the TD, TDR, and MRdata structures and transactions may be made by one of ordinary skill.

While the peripheral processor is passive in regards to opening andclosing various pipes, in conditions where the host processor is in alower power state (e.g., awake-low power, sleep-low power, etc.), theperipheral processor may “wake” the IPC layer, in order that the IPClayer may further “wake” the host processor for enabling and/or openingof a pipe specified by the peripheral processor, or for transferringdata from the peripheral to the host processor via an enabled pipe.

Exemplary Power Management Scheme

As a brief aside, existing PCIe implementations support a so-called“standby” or “sleep” mode (e.g., an awake-low power state, a sleep-lowpower state, etc.). However, the existing PCIe sleep mode operation wasdesigned for personal computer implementations which have sleep statesthat are less involved than techniques used in e.g., typical cellularphone devices, tablets, etc. Accordingly, existing PCIe specificationsmandate an exit latency that is much shorter than the actual exitlatency that most cellular devices can support (an unresponsiveperipheral processor would cause the host fabric to hang). In view ofthe limitations of existing PCIe implementations, the disclosed IPCenabled host and peripheral processors independently track and controlsleep mode operation so that the shared memory interface (MMIO) can be“gated off” during sleep mode operation until the sleeping processorwakes up (i.e., switches from a lower power state to a higher powerstate).

In one embodiment, the computer readable instructions, when executed byat least one of the first or second processors (102A, 102B) isconfigured to perform power management. In one exemplary implementation,power management between the two independent processors is configuredaccording to a sleep message (e.g., a power state message). One suchsleep message contains: (i) a target field that indicates whichprocessor (e.g., host or peripheral) the message is directed to, (ii) astate field that triggers the appropriate processor state machine toenter or exit a sleep mode (e.g., a sleep-low power state, an awake-lowpower state, etc.), (iii) a type field which identifies the messagetype, and (iv) a completion status field which indicates whether thesleep message is succeeded or failed. It will be appreciated that otherconfigurations (including less or more fields, and/or different orderingthereof) may be used consistent with the various aspects of the presentdisclosure.

When the host is ready to enter sleep, it informs the peripheralprocessor via a Host Enter Sleep Message, and the host may transition tosleep mode; thereafter, the peripheral processor may also independentlyenter sleep mode. If the peripheral processor needs to reestablishcommunication with host, it can request the host to wake-up via one ormore of the built-in or out-of-band mechanisms described herein, whichtriggers “wake” (e.g., switching from a lower power state to a higherpower state) of the IPC layer and subsequently “wake” of the hostprocessor. Once the host processor has woken, the host updates theperipheral with a Host Exit Sleep Message.

In some examples, if an error occurs in reestablishing communicationbetween the peripheral processor and the host processor (e.g.,unsuccessful downlink data packet transfer over the specified pipe,unsuccessful wake of the host processor, etc.), the peripheral processormay continuously or repeatedly request IPC layer and/or host “wake”,thereby preventing one or more of the IPC layer, the host processor, andthe peripheral processor from returning to a lower power state andincreasing overall power consumption of the device. Thus, it isdesirable in certain applications that the peripheral processor includea “wake-limiting” procedure to prevent continuous and/or repeated “wake”requests to the IPC layer and the host processor from the peripheralprocessor.

Exemplary Power Management Error Handling Scheme

In one aspect, the computer readable instructions, when executed by theperipheral processor (102B) are configured to limit the number of “wake”requests to the IPC layer and the host processor from the peripheralprocessor.

In one embodiment, the peripheral processor includes a wake-limitingprocedure, which prevents continuous and/or overly repetitive “wake”requests from the peripheral processor. As described herein, an energycost associated with switching from the sleep-low power state to theawake-high power state may be greater than an energy cost associatedwith switching from the awake-low power state to the awake-high powerstate. Accordingly, the IPC wake-limiting procedure may include firstidentifying a state of the host processor (e.g., the AP). Based on thecurrent state of the host processor, the peripheral processor may thenlimit the number of wake requests to the host processor for optimizationof power consumption.

Specifically, in a condition where the host processor switches to or isin the awake-low power state, existing or new downlink data packets aredetected on an enabled/opened pipe, and the host processor has initiateda read transaction on the pipe, the host processor is switched to theawake-high power state, and the downlink data transfer is executed.Alternatively, in a condition where the host processor switches to or isin the sleep-low power state and existing or new downlink data packetsare detected on an enabled/opened pipe, the peripheral processor islimited to a specified number of wake requests to the host processor fortransferring of the data. Thus, the exemplary wake-limiting proceduremay prevent continuous power consumption by the peripheral processor,the IPC layer, and/or the host processor caused by a transfer error(e.g., downlink data packet transfer error).

Methods

Various methods may be executed by apparatus 100 for managing powerduring normal operating conditions and during operating conditions wherethe host processor is entering or is in a lower power state (e.g., awakelow-power states, sleep-low power states, etc.) to limit the number of“wake” requests received from the peripheral processor. The apparatus100 may include integrated circuity configured to implement“intelligent” power and state management. The integrated circuitryincludes one or more semiconductive die with digital processor apparatusdisposed thereon and configured to communicate with one or more otherintegrated circuit devices within a common platform (e.g., mobilewireless device).

FIG. 4 is a logical flow diagram illustrating an exemplary embodiment ofa power management method 400 for independently operable processorsduring normal operating conditions.

As a brief aside, processor power consumption is affected by a plethoraof factors such as memory use, voltage, clock frequency, etc. Metricsfor power consumption typically incorporate computational efficacy; forexample, in the computing arts, performance can be benchmarked as numberof compute cycles per watt consumed. Accordingly, in various describedembodiments, when the relative processing performance is low relative tothe amount of power consumed (or based on other considerations), thevarious processors will prefer to operate in lower power states. Withinthis context, artisans of ordinary skill, given the contents of thepresent disclosure, will readily appreciate that there are a plethora ofactions and/or transactions which can be initiated by another processorwhich require action on the part of the processor. More directly, thepresent disclosure recognizes that the processor must consider one ormore other processor activities in order to properly assess the optimalpower strategy. Thus, the processor's determined preference for lowpower operation must in many cases be balanced against theconsiderations of the system as a whole.

At step 402 of the method 400, a processor determines when one or moreinternal considerations indicate that low power operation may bedesirable. In one exemplary embodiment, the processor monitors itscurrent processing load; when the processing load falls below a minimumthreshold, the processor flags an opportunity to reduce powerconsumption.

More complex embodiments may incorporate multiple processor-specificfactors; for example, such factors may include e.g., the processor'sstate machine, historic processing burden, anticipated processingburden, etc. Historic processing burden and/or anticipated processingburden may be based for example on an analysis of a histogram ofprocessing activity, and/or software execution which correlates withpower consumption. For instance, the presence of a pending data transfer(e.g., a DMA access) may indicate that the processor shouldpre-emptively prepare for active mode operation. Similarly, the presenceof a cache miss may signal that the processor has an opportunity tosleep while data is fetched from less accessible memory (e.g., a diskdrive, etc.).

Those of ordinary skill in the related arts will readily appreciate thatcertain applications may be adversely affected by performance lossesthat are attributable to excessive power optimization. Similarly, someusers prefer performance over power consumption, or vice versa. Stillfurther, some manufacturers prefer to ensure a minimum performance ormaximum power consumption so as to provide a certain product experienceto consumers. Accordingly, certain embodiments of the present disclosuremay additionally prioritize processor performance and/or powerconsumption against other considerations (e.g., user experience,latency, etc.). In some cases, priorities may be dynamically evaluatedand even altered.

In some implementations of the present disclosure, one or more relevantparameters are stored via dedicated hardware registers and/or hardwarelogic, etc. For example, user preferences and/or manufacturerpreferences may be stored within dedicated non-architectural registersand/or configured within logic. In other examples, the relevantparameters may be stored within memory (e.g., BIOS), or otherwisevirtualized. For example, a state machine may be implemented as avirtualized machine (e.g., the states, inputs, outputs, etc. are storedwithin memory). In some cases, the relevant parameters are stored via amemory mapped memory space such that other processors may freely accessthe processors parameters (for the other processor's own consideration,as discussed infra). Common examples of relevant parameters may includefor example, processing metrics, historic processing burden, indicia ofpredicted load, etc.

At step 404 of the method 400, the processor verifies that anotherprocessor(s) has not and/or will not trigger a condition that preventsreduced power operation. As previously noted, in some conditions,transactions via the inter-processor communications link can result in awake event. In other conditions, it may be advantageous to limit thenumber of transactions and prevent excessive power consumption caused byrepeatedly waking the processor from a lower power state.

In some embodiments of the present disclosure, the processor retrievesone or more relevant parameters associated with another processor thatare stored via dedicated hardware registers, hardware logic, memorymapped memory space, etc. Based on the one or more relevant parameters,the processor can determine the current state and/or predict the futureactivity of the other processor. In this manner, the processor canintelligently determine when to transition into/out of lower powerstates.

In some implementations, a system of processors may incorporate a powercontroller which tracks the power state of each of the processors of thesystem (as well as other potentially relevant considerations, such asthermal design power (TDP) margin or the like). In these centralizedpower controller systems, the processor may be able to determine thecurrent power state of each of the other processors by reading thecontents of the power controller. For example, in one such exemplaryembodiment, the power controller is mapped to a dedicated portion of thememory map.

In one implementation, based on the foregoing considerations of (i) theprocessor's load, and (ii) the other processor's current and/oranticipated traffic, the processor determines whether a reduced powermode is appropriate and if so, enters the appropriate reduced power mode(step 406).

In some embodiments, the processor must receive an acknowledgement orinstruction before it can transition to the reduced power mode. In onesuch variant, the host processor (or other power controlling entity)uses a sleep message to control sleep of the host and peripheralprocessor. An exemplary sleep message may include, without limitation: atarget that indicates which processor the message is targeting, a statethat identifies the reduced power mode (e.g., active or sleep state),and/or a type that is used to uniquely identify the message. In somecases, the peripheral processor may additionally respond with a sleepresponse message that includes a status to indicate success or failure.

For example, where the host processor transmits a sleep message to theperipheral processor having the target field set to the peripheralprocessor, then the peripheral processor will responsively enter or exitsleep mode in accordance with the sleep message. Where the hostprocessor transmits a sleep message to the peripheral processor havingthe target field set to the host processor, then the peripheralprocessor may accept the information as merely information with regardto the host processor's current state.

In related embodiments, the processor additionally notifies the otherprocessor(s) of its reduced power mode. In one exemplary implementation,the notification includes writing to a location in a shared memorymapped interface and issuing an interrupt that indicates the statusupdate.

In other implementations, the notification may be implemented viaregister writes, dedicated signaling, interrupt signaling, out-of-bandsignaling, etc. Still other implementations may not notify the otherprocessor; the other processor(s) may infer the status of the reducedpower processor, or alternatively query the reduced power processorstate (via a polling process, etc.) In systems with a centralized powercontroller, the processor may provide its power state information to thepower controller; subsequently thereafter, other processors candetermine the state of the processor by querying the power controller.Still other schemes will be readily appreciated by those of ordinaryskill in the related arts, given the contents of the present disclosure.

In an exemplary embodiment, the processor's state is controlled by astate machine having at least one sleep state, and at least one activestate. The state machine may provide an active state (e.g., anawake-high power state), a reduced power state (e.g., a sleep-low powerstate), and two transitionary states (e.g., awake-low power states).However, it is appreciated that the various aspects of the presentdisclosure are readily applicable to more complex schemes which mayinclude multiple power states having different associated powerconsumptions, capabilities, and/or performances associated therewith,etc. Common examples of reduced power states include without limitation,states that reduce the voltage and/or frequency of signaling and/orclocks, states that selectively enable or disable circuitry, states thatselectively enable or disable interfaces, etc.

In an exemplary embodiment, the reduced power notification may includeadditional information to assist other processors in maximizingperformance. Common examples of such information includes withoutlimitation: a minimum or maximum sleep time, an indication of thereduced power state (where there are multiple states), an indication ofthe wake-up latency, a starting time stamp, etc. For instance, beforewaking up the host processor, the peripheral processor may evaluate theamount of time that has elapsed since the host processor has powereddown (longer sleep times represent more power savings). Moreover, fornon-urgent traffic, the peripheral processor may buffer time-insensitivedata before waking the host processor. Still further, the peripheralprocessor can consider the wake-up latency so as to start the wakeprocess with enough lead time to minimize overall performance impact fortime critical transactions. Various other optimizations may besubstituted with equal success, such other optimizations recognized bythose of ordinary skill given the contents of the present disclosure.

In a related aspect, when the host processor sends reduced powernotifications (e.g., notification of switch from an awake-high powerstate to an awake-low power state, notification of switch from anawake-low power state to a sleep-low power state, etc.), the peripheralprocessor may determine whether or not to “wake” the host processor.Turning now to FIG. 5, a flow diagram illustrates a first exemplarymethod 500 for determining permissive “wake” of the host processor froman awake-low power state to an awake-high power state by activity onanother processor (e.g., a peripheral processor).

The method 500 may be executed when the host processor enters a lowerpower state. At step 502, the peripheral processor receives anotification that the host processor is switching to an awake-low powerstate.

At step 504, the peripheral processor determines that there is a pendingdownlink data packet on an IPC pipe. In one implementation, this isaccomplished by determining that the TDR or other data buffer associatedwith the IPC pipe is not empty and contains data for downlink transfer.

Next, at step 506, the peripheral processor determines that the hostprocessor has initiated a read transaction for the IPC pipe. At step508, the peripheral processor wakes the IPC layer and the host processorto perform the data transfer. In accordance with the method 500, the IPClayer and the host processor wakes up only when the host processor hasinitiated a read transaction for an IPC pipe.

FIG. 6 includes a flow diagram illustrating a second exemplary method600 for determining permissive “wake” of the host processor from anawake-low power state to an awake-high power state by activity onanother processor (e.g., a peripheral processor). In the illustratedembodiment, the method 600 is executed when a new downlink data packetis generated, and the host processor is in an awake-low power state.

At step 602, the peripheral processor determines that the host processoris in an awake-low power state. In one implementation, this isaccomplished by determining that the last sleep message received fromthe host processor was a message indicating that the host processor wasentering into the awake-low power state.

At step 604, the peripheral processor determines that a new downlinkdata packet is generated on an IPC pipe. In one implementation, this isaccomplished by detecting that the number of TDs in the TDR associatedwith the IPC pipe has been incremented. This indicates that a new TD hasbeen allocated to the new downlink data packet.

At step 606, the peripheral processor determines that the host processorhas initiated a read transaction for the IPC pipe. In oneimplementation, this is accomplished by determining that the hostprocessor has previously issued a read request to the peripheralprocessor for any subsequent data placed onto the IPC pipe for transferover to the host processor.

At step 608, the peripheral processor wakes the IPC layer and the hostprocessor. In one implementation, this is accomplished by sending aninterrupt (e.g., a MSI) to the host processor. In accordance with themethod 600, the IPC layer and the host processor wakes up only when thehost processor has initiated a read transaction for the IPC pipe havingthe newly generated downlink data packet.

FIG. 7 includes a flow diagram illustrating an example of operations 700of a wake-limiting procedure performed by a peripheral processor inorder to limit power consumption by the IPC link, the peripheralprocessor, and/or the host processor due to continuous and/or repeatedwake requests from the peripheral processor. The wake-limiting procedureis executed when the host processor enters a sleep-low power state orwhen a new downlink data packet is generated on an enabled IPC pipewhile the host processor is in the sleep-low power state.

Each downlink IPC pipe is associated with a wake-limiting counter and apre-defined wake limit threshold. The wake limit threshold indicates themaximum number of permissible “wakes” of the host processor by theperipheral processor each time a new downlink data packet is generatedon the IPC pipe while the host processor is in the sleep-low power stateor each time a downlink data packet has been transferred to the hostprocessor over the IPC pipe. The predefined wake limit threshold for anIPC pipe may be configured by the host processor at runtime or it may behard-coded in the peripheral processor at compile time. If the number ofwakes of the host processor exceeds the wake limit threshold, theperipheral processor is no longer permitted to wake the host processoruntil the wake-limiting counter is reset to zero. The wake-limitingcounter for each IPC pipe may be reset to zero in conditions where: (i)the IPC pipe becomes enabled by the host processor, (ii) a new downlinkdata packet is generated on the IPC pipe, or (iii) the existing downlinkdata packet is successfully transferred to the host processor.

Each downlink IPC pipe may be associated with e.g., a fatal error flagthat indicates whether exceeding the wake limit is treated as a fatalerror. The fatal error flag may be for instance configured by the hostprocessor at runtime, or it may be hard-coded in the peripheralprocessor at compile time. When a fatal error is triggered by an IPCpipe exceeding its wake limit, the device may take any appropriateaction for handling the fatal error, such as resetting the hostprocessor and/or the peripheral processor.

To determine whether to permit waking of the host processor, theperipheral processor checks whether there are any downlink packetspending on any enabled IPC pipes. Any such pipe is a wake-eligible pipe.The peripheral processor is permitted to wake the host processor whenthe wake-limiting counter is less than the wake limit threshold for anywake-eligible pipe. If the wake-limiting counter is not less than thewake limit threshold for any wake-eligible pipe and the fatal error flagis set, the peripheral processor triggers a fatal error to be handled bythe device. If the peripheral processor determines that wake ispermitted, the peripheral processor increments the wake-limiting counterfor each wake-eligible pipe if it is less than the wake limit threshold.

As shown in FIG. 7, the peripheral processor receives a sleep-low powernotification from the host processor (at step 702); or, while the hostprocessor is in the sleep-low power state, the peripheral processordetermines that a new downlink data packet is generated on an IPC pipe(at step 704). In response to step 702 or step 704 occurring, theperipheral processor sets the wake flag to “false” at step 706.

During process flow 708, the peripheral processor checks thewake-limiting counter for each enabled pipe with a pending downlink datapacket. At step 710, the peripheral processor determines whether thevalue of the wake-limiting counter is less than the wake limitthreshold. If the value of the counter is not less than thewake-limiting threshold, the peripheral processor determines whether thefatal error flag is set at step 712. If the fatal error flag is set, theperipheral processor triggers a fatal error at 714. Otherwise, theperipheral processor determines whether there are more pipes to check atstep 716.

If at step 710, the peripheral processor determines that the value ofthe counter is less than the wake limit threshold, the peripheralprocessor sets the wake flag to “true” at step 718 and increments thewake-limiting counter at step 720. The peripheral processor thendetermines whether there are more pipes to check at 716.

If the peripheral processor determines that there are more enabled pipeswith a pending downlink data packet at step 716, the peripheralprocessor repeats the process flow 708 for the next such pipe.Otherwise, the peripheral processor determines whether the wake flag isset to “true” at step 722. If the wake flag is set to “true”, theperipheral processor wakes the host processor at step 724. Otherwise,the peripheral processor is not permitted to wake the host processor atstep 726.

Returning to FIG. 4, thereafter, when one or more of the “wake”conditions described supra occurs, the processor exits the reduced powermode and may send a “wake” notification (step 408). Further, transfer ofdownlink and/or uplink data packets may occur between the host processorand the peripheral processor.

FIGS. 8A and 8B are data flow diagrams illustrating examples ofcommunications between a peripheral device, e.g., a baseband processor,and a host processor, e.g., an AP, during a Wake-Limiting Procedure. Forthe examples of FIG. 8, IPC pipes A and B are enabled for transferringdata between the baseband processor and the AP. The baseband processormay be e.g., a cellular or Wi-Fi peripheral processor that is in datacommunication with a network. In the examples of FIG. 8, the IPC pipe Amay be used to transfer, e.g., cellular data, and has a wake-limit oftwo (2). The IPC pipe B may be used to transfer, e.g., control data, andhas a wake-limit of three (3). Neither IPC pipe A nor IPC pipe B has thefatal error flag set; any pending downlink packets are held by thebaseband processor until the packet is transferred to the AP.

“Wake” requests are communicated from the baseband processor to the APto wake the AP into an awake-high power state. “Sleep” notifications arecommunicated from the AP to the baseband processor when the AP switchesto a sleep-low power state. The data flow of FIG. 8 will be described inconjunction with the operations 700 of FIG. 7.

During a period of time T1, the AP is in a sleep-low power state, andthe values of the wake-limiting counters for IPC pipes A and B are zero(0). The baseband processor receives new downlink data packets from thenetwork and places the new packets on IPC pipes A and B pending transferto the AP (step 704), which causes the baseband processor to perform theoperations 700 of the wake-limiting procedure. The baseband processorsets the wake flag to “false” (step 706) and performs the operations inthe process flow 708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is zero, which is less than pipe A's wake limit threshold oftwo. The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to one (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716), and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is zero, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718),and increments pipe B's wake-limiting counter to one (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During a period of time T2, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is one, which is less than pipe A's wake limit threshold of two.The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to two (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716) and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is one, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to two (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During a period of time T3, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). In this example, the value of pipe A'swake-limiting counter is two, which is not less than pipe A's wake limitthreshold of two. The baseband processor then determines that pipe A'sfatal error flag is not set (step 712) and that pipe B has a pendingdownlink data packet (step 716). The baseband processor proceeds withperforming the operations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is two, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to three (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During a period of time T4, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T4, each ofpipes A and B has a pending downlink packet to transfer to the AP.

During a period of time T5, the AP is in the sleep-low power state, andthe baseband processor receives a new downlink data packet from thenetwork for transfer to the AP over pipe A. In response to receiving thenew downlink data packet for transfer over pipe A, the basebandprocessor resets the wake-limiting counter for pipe A to zero and placesthe new packet on pipe A pending transfer to the AP (step 704), whichcauses the baseband processor to perform the operations 700 of thewake-limiting procedure. The baseband processor sets the wake flag to“false” (step 706) and performs the operations in the process flow 708for each of pipes A and B (pipe B still has a pending data transfer tothe AP).

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is zero, which is less than pipe A's wake limit threshold oftwo. The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to one (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716) and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three (because it was not reset), which is not less than pipeB's wake limit threshold of three. The baseband processor thendetermines that pipe B's fatal error flag is not set (step 712) and thatit has performed the process flow 708 for all enabled pipes with pendingdownlink data packets (step 716). The baseband processor checks the wakeflag (step 722) and because the wake flag is “true”, the basebandprocessor wakes the AP (step 724) by sending a wake request. In responseto the wake request, the AP switches from the sleep-low power state tothe awake-high power state. While the AP is in the awake-high powerstate, the AP may perform operations that do not include initiatingtransfers of the pending packets on pipes A and B.

During a period of time T6, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is one, which is less than pipe A's wake limit threshold of two.The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to two (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716) and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “true”, the baseband processor wakes the AP (step 724)by sending a wake request. In response to the wake request, the APswitches from the sleep-low power state to the awake-high power state.While the AP is in the awake-high power state, the AP may performoperations that do not include initiating transfers of the pendingpackets on pipes A and B.

During a period of time T7, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T7, pipe A hastwo pending downlink data packets to transfer to the AP, and pipe B hasone pending downlink data packet to transfer to the AP.

During time period T8, the AP is in the sleep-low power state, and thebaseband processor receives a new downlink data packet from the networkfor transfer to the AP over pipe B. In response to receiving the newdownlink data packet for transfer over pipe B, the baseband processorresets the wake-limiting counter for pipe B to zero, and places the newpacket on pipe B pending transfer to the AP (step 704), which causes thebaseband processor to perform the operations 700 of the wake-limitingprocedure. The baseband processor sets the wake flag to “false” (step706) and performs the operations in the process flow 708 for each ofpipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two (because pipe A's counter was not reset), which is notless than pipe A's wake limit threshold of two. The baseband processorthen determines that pipe A's fatal error flag is not set (step 712) andthat pipe B has a pending downlink data packet (step 716). The basebandprocessor proceeds with performing the operations in the process flow708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is zero, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to one (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T9, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the wake-limiting procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is one, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to two (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T10, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the wake-limiting procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is two, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to three (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T11, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the wake-limiting procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712), and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T11, pipe A hastwo pending downlink data packets to transfer to the AP, and pipe B hastwo pending downlink data packets to transfer to the AP.

During time period T12, the baseband processor receives a wakenotification and then a sleep notification from the AP (step 702), whichcauses the baseband processor to perform the operations 700 of thewake-limiting procedure. The baseband processor sets the wake flag to“false” (step 706). Because both pipes A and B have pending downlinkdata packets to transfer to the AP, the baseband processor performs theoperations in the process flow 708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712), and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T12, pipe A hastwo pending downlink data packets to transfer to the AP, and pipe B hastwo pending downlink data packets to transfer to the AP.

Referring to FIG. 8B, during time period T13, the AP switches from thesleep-low power state to the awake-high power state and sends a wakenotification to the baseband processor. The AP then initiates a transferof a pending downlink data packet on pipe A from the baseband processorto the AP, which causes the pending downlink data packet on pipe A to betransferred from the baseband processor to the AP. In response to apending downlink data packet being transferred from the basebandprocessor to the AP over pipe A, the baseband processor resets thewake-limiting counter for pipe A to zero.

During a period of time T14, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706) and performsthe operations in the process flow 708 for each of pipes A and B (bothpipes still have pending data to transfer to the AP).

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is zero, which is less than pipe A's wake limit threshold oftwo. The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to one (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716) and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three (because it was not reset), which is not less than pipeB's wake limit threshold of three. The baseband processor thendetermines that pipe B's fatal error flag is not set (step 712) and thatit has performed the process flow 708 for all enabled pipes with pendingdownlink data packets (step 716). The baseband processor checks the wakeflag (step 722) and because the wake flag is “true”, the basebandprocessor wakes the AP (step 724) by sending a wake request. In responseto the wake request, the AP switches from the sleep-low power state tothe awake-high power state. While the AP is in the awake-high powerstate, the AP may perform operations that do not include initiatingtransfers of the pending packets on pipes A and B.

During a period of time T15, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is one, which is less than pipe A's wake limit threshold of two.The baseband processor sets the wake flag to “true” (step 718) andincrements pipe A's wake-limiting counter to two (step 720). Thebaseband processor determines that pipe B has a pending downlink datapacket (step 716) and performs the operations in the process flow 708for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “true”, the baseband processor wakes the AP (step 724)by sending a wake request. In response to the wake request, the APswitches from the sleep-low power state to the awake-high power state.While the AP is in the awake-high power state, the AP may performoperations that do not include initiating transfers of the pendingpackets on pipes A and B.

During a period of time T16, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T16, pipe A hasone pending downlink data packet to transfer to the AP, and pipe B hastwo pending downlink data packets to transfer to the AP.

During time period T17, the AP switches from the sleep-low power stateto the awake-high power state and sends a wake notification to thebaseband processor. The AP then initiates a transfer of a pendingdownlink data packet on pipe B from the baseband processor to the AP,which causes the pending downlink data packet on pipe B to betransferred from the baseband processor to the AP. In response to apending downlink data packet being transferred from the basebandprocessor to the AP over pipe B, the baseband processor resets thewake-limiting counter for pipe B to zero.

During time period T18, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706) and performsthe operations in the process flow 708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two (because pipe A's counter was not reset), which is notless than pipe A's wake limit threshold of two. The baseband processorthen determines that pipe A's fatal error flag is not set (step 712) andthat pipe B has a pending downlink data packet (step 716). The basebandprocessor proceeds with performing the operations in the process flow708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is zero, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to one (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T19, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is one, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to two (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T20, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is two, which is less than pipe B's wake limit threshold ofthree. The baseband processor sets the wake flag to “true” (step 718)and increments pipe B's wake-limiting counter to three (step 720). Thebaseband processor determines that it has performed the process flow 708for all enabled pipes with pending downlink data packets at step 716.The baseband processor checks the wake flag (step 722) and because thewake flag is “true”, the baseband processor wakes the AP (step 724) bysending a wake request. In response to the wake request, the AP switchesfrom the sleep-low power state to the awake-high power state. While theAP is in the awake-high power state, the AP may perform operations thatdo not include initiating transfers of the pending packets on pipes Aand B.

During time period T21, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseboth pipes A and B have pending downlink data packets to transfer to theAP, the baseband processor performs the operations in the process flow708 for each of pipes A and B.

For pipe A, the baseband processor checks the value of the pipe A'swake-limiting counter (step 710). The value of pipe A's wake-limitingcounter is two, which is not less than pipe A's wake limit threshold oftwo. The baseband processor then determines that pipe A's fatal errorflag is not set (step 712) and that pipe B has a pending downlink datapacket (step 716). The baseband processor proceeds with performing theoperations in the process flow 708 for pipe B.

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three, which is not less than pipe B's wake limit thresholdof three. The baseband processor then determines that pipe B's fatalerror flag is not set (step 712) and that it has performed the processflow 708 for all enabled pipes with pending downlink data packets (step716). The baseband processor checks the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726). At the end of the period of time T21, pipe A hasone pending downlink data packet to transfer to the AP, and pipe B hasone pending downlink data packet to transfer to the AP.

During time period T22, the AP switches from the sleep-low power stateto the awake-high power state and sends a wake notification to thebaseband processor. The AP then initiates a transfer of a pendingdownlink data packet on pipe A from the baseband processor to the AP,which causes the pending downlink data packet on pipe A to betransferred from the baseband processor to the AP. In response to apending downlink data packet being transferred from the basebandprocessor to the AP over pipe A, the baseband processor resets thewake-limiting counter for pipe A to zero.

During a period of time T23, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706) and performsthe operations in the process flow 708 for pipe B (only pipe B still haspending data to transfer to the AP).

For pipe B, the baseband processor checks the value of the pipe B'swake-limiting counter (step 710). The value of pipe B's wake-limitingcounter is three (because it was not reset), which is not less than pipeB's wake limit threshold of three. The baseband processor thendetermines that pipe B's fatal error flag is not set (step 712) and thatit has performed the process flow 708 for all enabled pipes with pendingdownlink data packets (step 716). The baseband processor checks the wakeflag (step 722) and because the wake flag is “false”, the basebandprocessor is not permitted to wake the AP (step 726). At the end of theperiod of time T23, pipe A has no pending downlink data packets totransfer to the AP, and pipe B has one pending downlink data packet totransfer to the AP.

During time period T24, the AP switches from the sleep-low power stateto the awake-high power state and sends a wake notification to thebaseband processor. The AP then initiates a transfer of a pendingdownlink data packet on pipe B from the baseband processor to the AP,which causes the pending downlink data packet on pipe B to betransferred from the baseband processor to the AP. In response to apending downlink data packet being transferred from the basebandprocessor to the AP over pipe B, the baseband processor resets thewake-limiting counter for pipe B to zero.

During a period of time T25, the baseband processor receives a sleepnotification from the AP (step 702), which causes the baseband processorto perform the operations 700 of the Wake-Limiting Procedure. Thebaseband processor sets the wake flag to “false” (step 706). Becauseneither pipe A nor pipe B has a pending data transfer, the basebandprocessor proceeds with checking the wake flag (step 722) and becausethe wake flag is “false”, the baseband processor is not permitted towake the AP (step 726).

It will be readily appreciated by those of ordinary skill that differentcombinations and/or variations of the foregoing can be made, dependingon the desired application and performance attributes.

Moreover, it will be recognized that while certain implementations andembodiments are described in terms of a specific sequence of steps of amethod, these descriptions are only illustrative of the broaderprinciples and architectures presented herein, and may be modified asrequired by the particular application. Certain steps may be renderedunnecessary or optional under certain circumstances. Additionally,certain steps or functionality may be added to the disclosedembodiments, or the order of performance of two or more steps permuted.All such variations are considered to be encompassed and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the disclosure as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the disclosure. Theforegoing description is of the best mode presently contemplated ofcarrying out the principles and architectures presented herein. Thisdescription is in no way meant to be limiting, but rather should betaken as illustrative of the general principles of the disclosure. Thescope should be determined with reference to the claims.

What is claimed is:
 1. A method performed by a first device to limitwake requests to a second device, the method comprising: detecting acondition for determining whether to send a wake request to the seconddevice; determining that one or more data units are to be transferredfrom the first device to the second device over one or more data lines;for each data line of the one or more data lines, determining whetherone or more previous wake requests associated with the data line meet aprescribed criterion; and in response to determining that at least oneof the data lines is associated with one or more previous wake requestsmeeting the prescribed criterion, sending a wake request to the seconddevice.
 2. The method of claim 1, wherein detecting the condition fordetermining whether to send the wake request to the second devicecomprises detecting that the second device has switched from a firstpower state to a second, lower power state.
 3. The method of claim 1,wherein detecting the condition for determining whether to send the wakerequest to the second device comprises determining that a new data unitis to be transferred from the first device to the second device over afirst data line of the one or more data lines.
 4. The method of claim 3,wherein the prescribed criterion comprises a number of prior wakerequests, and the method further comprises: in response to determiningthat the new data unit is to be transferred from the first device to thesecond device over the first data line, setting a number of previouswake requests associated with the first data line to zero.
 5. The methodof claim 1, wherein the prescribed criterion comprises a number of priorwake requests, and the method further comprises: for each data line ofthe one or more data lines, detecting that the data line is enabled andsetting a number of previous wake requests associated with the data lineto zero.
 6. The method of claim 1, wherein the prescribed criterioncomprises a number of prior wake requests, and the method furthercomprises: in response to determining that a first data unit of the oneor more data units is transferred from the first device to the seconddevice over a first data line of the one or more data lines, setting anumber of previous wake requests associated with the first data line tozero.
 7. The method of claim 1, wherein the prescribed criterioncomprises a number of prior wake requests, and the method furthercomprises: in response to determining that at least one of the datalines is associated with a number of previous wake requests that is lessthan the wake limit threshold, incrementing the number of previous wakerequests associated with each of the at least one of the data lines. 8.Processor apparatus adapted for use in a portable device, the processorapparatus comprising: a first digital processor; and storage apparatusin data communication with the first digital processor, the storageapparatus comprising a plurality of computer readable instructionsconfigured to, when executed by the first digital processor, cause thefirst digital processor to: determine that one or more data units are tobe transferred from the first processor to the second processor over oneor more data lines; for each data line of the one or more data lines,determine whether a number of previous wake requests associated with thedata line is less than a wake limit threshold; and in response todetermining that at least one of the data lines is associated with anumber of previous wake requests that is less than the wake limitthreshold, send a wake request to the second processor.
 9. The processorapparatus of claim 8, wherein the plurality of computer readableinstructions are further configured to, when executed by the firstdigital processor, cause the first digital processor to detect acondition for determination whether to send the wake request to thesecond processor, the detection comprising detection that the secondprocessor has switched from a first power state to a second, lower powerstate.
 10. The processor apparatus of claim 8, wherein the plurality ofcomputer readable instructions are further configured to, when executedby the first digital processor, cause the first digital processor to, inresponse to a determination that one or more new data units is to betransferred from the first processor to the second processor over thefirst data line, set a number of previous wake requests associated withthe first data line to zero.
 11. The processor apparatus of claim 8,wherein the plurality of computer readable instructions are furtherconfigured to, when executed by the first digital processor, cause thefirst digital processor to: for each data line of the one or more datalines, detect that the data line is enabled, and set a number ofprevious wake requests associated with the data line to zero.
 12. Theprocessor apparatus of claim 8, wherein the plurality of computerreadable instructions are further configured to, when executed by thefirst digital processor, cause the first digital processor to: inresponse to a determination that a first data unit of the one or moredata units is transferred from the first processor to the secondprocessor over a first data line of the one or more data lines, set anumber of previous wake requests associated with the first data line tozero.
 13. The processor apparatus of claim 8, wherein the plurality ofcomputer readable instructions are further configured to, when executedby the first digital processor, cause the first digital processor to: inresponse to a determination that at least one of the data lines isassociated with a number of previous wake requests that is less than thewake limit threshold, increment the number of previous wake requestsassociated with each of the at least one of the data lines.
 14. Aportable electronic device configured for power management, the portableelectronic device comprising: a first processor; a second processor indata communication with the first processor via one or more data lines;and storage apparatus in data communication with at least the firstdigital processor, the storage apparatus comprising a plurality ofcomputer readable instructions configured to, when executed by the firstdigital processor, cause the first digital processor to: upon receipt ofdata indicating a state change, determine that one or more data unitsare to be transferred from the first processor to the second processorover the one or more data lines; for each data line of the one or moredata lines, determine that a number of previous wake requests associatedwith the data line is less than a wake limit threshold; and based atleast on the determination that at least one of the data lines isassociated with a number of previous wake requests less than the wakelimit threshold, send a wake request to the second processor.
 15. Theprocessor apparatus of claim 14, wherein the data indicating a possiblestate change comprises data indicating that the second processor hasswitched from a first power state to a second, lower power state. 16.The processor apparatus of claim 14, wherein the data indicating a statechange comprises data indicating that that one or more new data unitsis/are queued to be transferred from the first processor to the secondprocessor over a first data line of the one or more data lines.
 17. Theprocessor apparatus of claim 16, wherein the plurality of computerreadable instructions are further configured to, when executed by thefirst digital processor and in response to a determination that the newdata unit is to be transferred from the first processor to the secondprocessor over the first data line, set a number of previous wakerequests associated with the first data line to zero.
 18. The processorapparatus of claim 14, wherein the plurality of computer readableinstructions are further configured to, when executed by the firstdigital processor, cause the first digital processor to: for each dataline of the one or more data lines, detect that the data line is enabledand setting a number of previous wake requests associated with the dataline to zero.
 19. The processor apparatus of claim 14, wherein theplurality of computer readable instructions are further configured to,when executed by the first digital processor, cause the first digitalprocessor to: in response to a determination that a first data unit ofthe one or more data units is transferred from the first processor tothe second processor over a first data line of the one or more datalines, set a number of previous wake requests associated with the firstdata line to zero.
 20. The processor apparatus of claim 14, wherein theplurality of computer readable instructions are further configured to,when executed by the first digital processor, cause the first digitalprocessor to: in response to a determination that at least one of thedata lines is associated with a number of previous wake requests that isless than the wake limit threshold, increment the number of previouswake requests associated with each of the at least one of the datalines.